Over the last fifty years, digital communication between electronic devices has become prevalent in modern technology. As more electronic devices speak with each other, it has become desirable to develop a common language of communication, in other words, a communication protocol. The communication protocol comprises a set of standard rules regulating how a pair of electronic devices communicate with each other and includes functions commonly needed during communication.
A multilayer communication protocol, for example, the Transmission Control Protocol and the Internet Protocol (TCP/IP), may comprise a plurality of layers for managing the respective functions of the protocol. For example, in the TCP/IP, the layers comprise, from top to bottom, an application layer, a transport layer, a network/internet layer, a data link layer, and a physical layer. Each layer of the protocol may be responsible for a defined set of functions used in the protocol and may be further subdivided into sublayers, for example, the data link layer comprises a Media Access Control (MAC) layer.
In the multilayer communication protocol, each layer operates independently of the other layers. This regime of independence for each layer provides for modular design and maintenance. In other words, updates in the functions of one layer may not require propagation of changes into the other layers. Each layer may interact with an adjacent layer, the lower layer providing services to the upper layer. In this manner, a lower layer, for example, the physical layer, may directly communicate with an upper adjacent layer, for example, a data link layer. The physical layer may communicate with a non adjacent upper layer, for example, the application layer, only by communicating through the intervening layers.
Recently, the communications industry has integrated satellite communication links into the Internet, which runs on the multilayered TCP/IP. Communication satellites are an important element of communication networks and provide accessibility for locations lacking hardwired access to networks, for example, the Internet. A typical satellite communication link comprises a first ground terminal communicating with a second ground terminal via the satellite. The first ground terminal transmits a signal to the satellite (uplink-return link), which then rebroadcasts the signal to the second ground terminal (downlink-forward link) and vice versa. The satellite communication link comprises a natural broadcast medium, which gives it several advantages over terrestrial wired networks.
To enhance standardization of multimedia satellite communication, Digital Video Broadcast (DVB) standards were developed for satellite communication. For example, the DVB-S2 forward link standard is a second generation specification for satellite broadband applications, and the DVB-RCS standard is a return specification. The DVB-S2 standard utilizes recent developments in coding and modulation that approach the Shannon bound for channel capacity. According to the DVB-S2 standard, the coding and modulation may be applied in an adaptive manner for one-to-one links to provide mitigation against signal fading, for example, rain fade.
Although satellites may provide robust communication to areas inaccessible to traditional terrestrial communication, satellite communication may be subject to certain drawbacks. One possible drawback is that inclement weather may degrade the quality of the signal, for example, rain fade. Rain fade comprises absorption of a microwave radio frequency downlink or uplink signal by rain or snow, and may be problematic at frequencies above 11 GHz. As will be appreciated by those skilled in the art, satellites with a low look angle are particularly subject to rain fade and may be subject to degraded satellite communication even when the weather at a ground terminal receiving the satellite signal is favorable.
Several methods have been disclosed that involve some form of cross layer protocol approach for improving satellite communication signal quality. For example, Peng et al., “Cross-layer enhancements of TCP Split-Connections Over Satellite Links”, Int'l J. Satellite Communication and Networking, 2006, volume 24, the entire contents of which are incorporated by reference herein, discloses a congestion control method for TCP selective acknowledgment split-connections applied to a satellite link between two protocols. The method provides a congestion notification from the MAC layer to the TCP layer in the protocol. Another cross layer method is disclosed by Chini et al. in the article “Dynamic Resource Allocation Based on a TCP-MAC Cross-layer Approach for Interactive Satellite Networks”, Int'l J. Satellite Communication and Networking, 2006, volume 24, the entire contents of which are incorporated by reference herein. This method for resource allocation in the return channel of a DVB-RCS standard network is based upon the cross layer interaction between the TCP and MAC layers.
However, with the recent push to use the Internet for multimedia applications that require low error rate, low delay, low delay variation, and low jitter, there may be drawbacks to integrating satellite links into the Internet with this kind of traffic. In these applications, the first and second ground terminals may comprise a first and second plurality of ground terminals. Satellite uplink and downlink bandwidth is limited and is typically distributed to the first and second pluralities of ground terminals, some of which may be transmitting and receiving traffic with varying levels of desired quality of service (QoS). The occurrence of rain fade may cause more difficulty in distributing bandwidth since the satellite uplink and downlink bandwidth decreases. Signal degradation may be particularly problematic for satellite downlink bandwidth since downlink bandwidth is several times smaller than uplink bandwidth, which benefits from greater transmission power.